Alkaline cell with improved high rate capability

ABSTRACT

The present disclosure relates generally to an alkaline electrochemical cell, such as a battery, and in particular to an improved gelled anode suitable for use therein. More specifically, the present disclosure relates to a gelled anode that improves anode discharge efficiency by adjusting physical properties such as apparent density.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to an alkaline electrochemicalcell, such as a battery, and in particular to an improved gelled anodesuitable for use therein. More specifically, the present disclosurerelates to a gelled anode that improves anode discharge efficiency byadjusting physical properties such as apparent density.

BACKGROUND OF THE DISCLOSURE

Alkaline electrochemical cells, commonly known as “batteries,” are usedto power a wide variety of devices used in everyday life. For example,devices such as radios, toys, cameras, flashlights, and hearing aids allordinarily rely on one or more electrochemical cells to operate. Thesecells produce electricity by electrochemically coupling, within thecell, a reactive gelled metallic anode, most commonly a zinc-containinggelled anode, to a cathode through a suitable electrolyte, such as apotassium hydroxide solution.

High rate discharge performance for cells in devices is partly dependenton the availability of sufficient anode reaction sites in the vicinityof the anode-cathode interface. This can be accomplished by increasingthe level of fine particles in the anode; however, increasing the levelof fines has a limit to improving performance because the dischargeproduct around the fine particles disrupts particle-to-particle contactand also tends to suppress ion diffusion. Ion diffusion can be anessential step to sustain fast anode-cathode reactions demanded by highdrain rates.

In view of the foregoing, the need exists for an anode that improves thedischarge rate capability of alkaline cells.

SUMMARY OF THE DISCLOSURE

Briefly, therefore, the present disclosure is directed to an alkalineelectrochemical cell comprising a cathode; a gelled anode mixture, themixture comprising an anode active material, a gelling agent, and analkaline electrolyte, wherein the anode active material has an apparentdensity of from about 2.50 g/cc to about 3.00 g/cc; and, a separatorbetween the cathode and the anode.

The present disclosure is also directed to a gelled anode mixturecomprising an anode active material, a gelling agent, and an alkalineelectrolyte, wherein the anode active material has an apparent densityof from about 2.50 g/cc to about 3.00 g/cc.

Other objects and features will be in part apparent and in part pointedout hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-section of an exemplary embodiment of anelectrochemical cell in accordance with the present disclosure.

FIG. 2 shows graphical depictions of digital still camera performancesincluding anodes in accordance with the present disclosure.

FIG. 3 shows graphical depictions of the cell amperage of exemplarycells including anodes in accordance with the present disclosure afterdrop tests.

FIG. 4 shows graphical depictions of the cell amperage of exemplarycells including anodes in accordance with the present disclosure beforedrop tests.

FIG. 5 shows graphical depictions of the partial discharge gassing ofexemplary cells including anodes in accordance with the presentdisclosure.

FIG. 6 is a graphical depiction of the digital still camera performanceof exemplary cells including anodes having different apparent densitiesafter three months of storage.

FIG. 7A is a micrograph of the particle size distribution of anexemplary anode active material having an apparent density of 2.71 g/cc.FIG. 7B is a micrograph of the particle size distribution of anexemplary anode active material having an apparent density of 2.95 g/cc.

FIG. 8A depicts the aspect ratio of an exemplary anode active materialin accordance with the present disclosure at an apparent density of 2.71g/cc. FIG. 8B depicts the aspect ratio of an exemplary anode activematerial in accordance with the present disclosure at an apparentdensity of 3.04 g/cc.

FIG. 9 depicts the aspect ratio of an exemplary anode active material inaccordance with the present disclosure at an apparent density of 2.68g/cc.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure is directed to improving the discharge ratecapability of cells, such as alkaline cells. The disclosure is alsoaimed at improving the anode discharge efficiency of cells by adjustingphysical properties of the cells, such as the apparent density of theanode active material. For example, this disclosure is generallydirected to improving anode active material properties, such as apparentdensity, to enhance the anode discharge efficiency at high drains ofdischarge.

I. General Electrochemical Cell Structure

Referring now to FIG. 1, an electrochemical cell is shown in the form ofa AA-size cylindrical cell battery and is generally indicated at 2. Itis contemplated, however, that the electrochemical cell of the presentdisclosure has applications to other sized batteries (e.g., AA−, AAA−,C− and D−), as well as to non-cylindrical cells, such as flat cells(e.g., prismatic cells and button cells) and rounded flat cells (e.g.,having a racetrack cross-section). The cylindrical cell configurationshown in FIG. 1 has a positive terminal 14, a negative terminal 6, and apositive current collector in the form of an electrically conductivecylindrical container 8. In the illustrated electrochemical cell, asingle piece formed container 8 may be of drawn steel having a closedbottom formed by an end wall 10 and a cylindrical side wall 12 formed asone piece with the end wall 10. The positive terminal 14 is thus definedby the end wall 10 of the metal container 8 in the illustratedembodiment. However, in alternative embodiments, the end wall may beflat and have a positive terminal plate (not shown) attached thereto asby welding to define the positive terminal 14 without departing from thescope of this disclosure. The opposite end of the container 8 isgenerally open. As used herein the term “side wall” refers not only to awall like the illustrated cylindrical wall 12 having a single,continuous curve, but also to side walls (not shown) having other shapesincluding those formed from multiple flat wall sections.

Contained in the container is a cathode 16 comprised of one or moreannular rings formed of a suitable cathode material which defines anopen center along the longitudinal direction of the container. Thecathode 16 may suitably have an outer diameter that is slightly greaterthan the inner diameter of the container side wall 12, to provide atight fit upon insertion of the cathode into the container 8. A suitablecoating, such as carbon, may be applied to the inner surface of thecontainer side wall 12 to enhance electrical contact between the cathode16 and the container 8. The cathode may comprise any number of variouscomponents, including for example an oxide of copper, manganese dioxide(e.g., electrolytic manganese dioxide), or other suitable cathodematerials.

Also contained in the container of FIG. 1 is a gelled anode 18, asfurther detailed elsewhere herein, which is located on the innerdiameter of a separator 20 so that the separator physically separatesthe gelled anode 18 from the cathode 16. The gelled anode 18, as furtherdetailed elsewhere herein, can be formed in any suitable manner, and maysuitably comprise a mixture including an anode metal (e.g., zinc)provided as a powder, an aqueous alkaline electrolyte and a highlycrosslinked, polyacrylic acid gelling agent. Examples of anode 18formulations, which may be generally suitable for use in accordance withthe present disclosure, are further detailed elsewhere herein.Additional electrolyte (not shown) may be added to the container 8during cell fabrication to further, or partially, wet the anode 18, thecathode 16 and the separator 20. Suitable electrolytes include, forexample, potassium hydroxide, sodium hydroxide, and/or lithiumhydroxide, in an alkaline battery, but other compositions can be usedwithout departing from the scope of the present disclosure.

To finally assemble the electrochemical cell, the cathode 16, separator20 and anode 18 are loaded into the container 8 with the container inits open configuration as shown. A sealing assembly 22, negative currentcollector 24 and negative terminal plate 28 are placed in the open upperend of the container 8 with the sealing assembly 22 seating on theshoulder 23 formed at the junction of the upper and lower extents 27, 29of the container and the negative terminal plate 28 seated on theshoulder formed in the sealing assembly 22.

It is to be noted that the term “longitudinal”, as used herein, refersto the general direction extending from one end of the container 8 tothe other, regardless of whether the greatest dimension of the containeris in the longitudinal direction. The terms “lateral,” “transverse” and“radial” refer to a general direction extending perpendicular to thelongitudinal direction so as to extend through the side wall 12 of thecontainer 8. In particular, where the term radial is used herein inreference to annular or circular shaped elements, it is understood thatthe terms lateral and transverse may be substituted for the radialcomponents that are other than annular or circular.

It is to be further noted that the electrochemical cell of the presentdisclosure is typically illustrated in a generally vertical orientation,with the positive terminal at the bottom and the negative terminal atthe top. Accordingly, use of terms herein such as top, bottom, upper andlower, are in reference to positions along the longitudinal direction ofthe cell 2 (e.g., of the container 8), while the use of terms such asinner and outer are in reference to positions along the transverse orradial direction.

II. Gelled Anode

As previously noted, the present disclosure is generally directed to agelled anode, and/or an electrochemical cell comprising such a gelledanode, which comprises a gelling agent (as further detailed elsewhereherein), an alkaline electrolyte (e.g., an aqueous potassium hydroxidesolution), and an anode active material (e.g., a material typicallycomprising zinc). The gelling agent is present in the anode, at least inpart, to add mechanical structure and/or to coat the metallic particlesto improve ionic conductivity within the anode during discharge. Thepreparation of the gelled anode is further detailed elsewhere herein;generally speaking, however, the gelled anode may be prepared bypreparing an electrolyte, preparing a coated metal anode which includesthe gelling agent, and then combining the electrolyte and the coatedmetal anode to form a gelled anode.

In this regard it is to be noted that, as used herein, “gelled anode”(as well as variations thereof) generally refers to the anode once theelectrolyte (or in some instances the remaining portion of theelectrolyte) has been added or introduced thereto. In contrast, a“coated metal anode” (as well as variations thereof) generally refers tothe anode prior to addition or introduction of the electrolyte thereto(or the full amount of the electrolyte thereto).

A. Anode Active Material

1. Active Material

The type of the anode active material may generally be selected fromthose known in the art, in order to optimize performance of the alkalineelectrochemical cell of which this gelled anode is a part. In someembodiments, the anode active material comprises zinc, which may be usedalone or in combination with one or more other metals. Furthermore, itis typically used in the form of an alloy powder. Thus, in someembodiments the anode active material comprises a zinc alloy.

For example, in one or more embodiments one of ordinary skill in the artmay readily select a suitable powder comprising zinc mixed with, oralloyed with, one or more other metals known in the art (e.g., In, Bi,Ca, Al, Pb, etc.). Accordingly, in this regard it is to be noted that,as used herein, “anode active material” and/or “zinc” may refer to aparticle or powder alone, or one that has been optionally mixed oralloyed with one or more other metals. Anode active material particlesmay be present in a variety of forms including, for example, elongated,round, as well as fiber-like or flake-like particles.

In some embodiments, the anode active material is in powder form that isa disk atomized type powder produced by a spinning disk process. Thismethod of processing can produce desired shapes and particlemorphologies, including elongated and round anode active materialparticles. The level of elongated and/or round particles can bemodulated as necessary with this method by adjusting the operatingparameters to make the powder. Some level of spherical shaped particlescan serve to provide good processing and the anode gel mixture will flowbetter in the presence of these particles. In other embodiments, airatomization is used to prepare the anode active material particles.Elongated particles, among other shapes, can also be produced when theair atomization process is used.

In some embodiments of the present disclosure, the zinc alloy comprisesindium and bismuth. In some embodiments of the present disclosure, thezinc alloy comprises from about 80 ppm to about 250 ppm of bismuth, insome embodiments about 120 ppm of bismuth, and in other embodimentsabout 200 ppm of bismuth. In other embodiments of the presentdisclosure, the zinc alloy comprises from about 80 ppm to about 250 ppmof indium, in some embodiments about 120 ppm of indium, and in otherembodiments about 200 ppm of indium. In yet other embodiments of thepresent disclosure, the zinc alloy comprises about 120 ppm of indium andabout 120 ppm of bismuth. In still other embodiments of the presentdisclosure the zinc alloy comprises about 200 ppm of indium and about200 ppm of bismuth. In other embodiments of the present disclosure, thezinc alloy comprises from about 80 ppm to about 250 ppm of bismuth andfrom about 80 ppm to about 250 ppm of indium.

In alternative embodiments of the present disclosure, the zinc alloycomprises lead. In some embodiments of the present disclosure, the zincalloy comprises from about 350 ppm to about 600 ppm of lead, in someembodiments about 425 ppm of lead, and in other embodiments about 500ppm of lead. In other embodiments, the zinc alloy comprises aluminum. Insome embodiments of the present disclosure, the zinc alloy comprisesfrom about 80 ppm to about 250 ppm of aluminum, in some embodimentsabout 100 ppm of aluminum, and in other embodiments about 200 ppm ofaluminum. In still other embodiments of the present disclosure, the zincalloy comprises bismuth and lead. In other embodiments, the zinc alloycomprises bismuth, indium and aluminum.

It is to be noted, however, that the type and/or concentration of theanode active material, and/or the electrolyte, may be affected by theselections made with respect to the other components of theelectrochemical cell, such as for example the cathode. For example,conventional cathodes, such as those having MnO₂ as an activeingredient, may consume more water by the cathodic reaction than isprovided by the electrolyte. The anodes of conventional alkaline cellsare thus generally limited to an active material concentration, orloading, that is below about 70 wt %, based on the weight of the anode,because higher loadings may not discharge efficiently, as the anodewould not contain sufficient quantities of electrolyte to properlysustain the water consuming reaction in the cathode. Furthermore, highactive material loadings with conventional particle size distributionsresult in higher mass transfer polarization due to the low porosity ofthese anodes, leading to early anode passivation and premature failure.

Conventional anode active materials may contain particles having a widedistribution of particle sizes, which range for example from a fewmicrons (e.g., about 5 microns, about 10 microns, about 15 microns,about 25 microns or up) up to about 500 microns, about 750 microns oreven about 1000 microns. Typically, however, most of the particles ofthe anode active material fall within a size distribution rangingbetween about 25 microns and about 500 microns.

Additionally, it may be advantageous to employ an anode active materialwhich has a smaller particle size, and/or a narrower particle sizedistribution. For example, it may be useful in one or more embodimentsof the disclosure if the anode active material particles having a sizedistribution wherein at least about 70%, about 75%, about 80%, about85%, about 90%, about 95% or even about 100% of the particles have astandard mesh-sieved particle size that is within about ±200 microns,about ±150 microns, about ±100 micron size range or less (e.g., about 90microns, about 70 microns, about 50 microns or less) of a given targetparticle size (e.g., about 50 microns, about 100 microns, about 150microns, about 200 microns, about 250 microns, or about 300 microns).For example, in one or more embodiments, it may be advantageous to useanode active material particles wherein between about 90% and 95%, oreven about 100%, of the particle sizes, by weight, are within about a200, 150, or even 100 microns of a target particle size of about 50microns, about 100 microns, about 150 microns, about 200 microns, about250 microns, or about 300 microns.

In this regard one skilled in the art will recognize that mesh sizescorresponding to these particle sizes can be identified using ASTMDesignation B214-99. An anode containing active material particleshaving a more narrow particle size distribution, such as those notedabove, may be well-suited for use in combination with, for example, acopper oxide-containing cathode, as detailed elsewhere herein, becausesuch a cathode is one example of a cathode that consumes less water thanalkaline manganese dioxide cells. Such an anode may be “drier” thanconventional electrochemical cells, meaning that the anode has a higherloading of anode active material particles that can be efficientlydischarged with reduced electrolyte concentrations. Such ananode/cathode combination may be particularly advantageous because, dueto the copper oxide, or a mixed copper oxide, active material in thecathode is low-water consuming, and thus the amount of electrolyterequired in the anode may be reduced relative to, for example, aconventional zinc manganese dioxide alkaline cell. The low-waterconsuming reaction advantageously permits an increase in anode activematerial loading in the anode and thereby facilitates a longer cellservice life.

Another factor that may impact cell performance relates to the surfacearea of the anode, with smaller particles typically increasing theeffective surface area of the anode. More specifically, increasing theactive anode electrode surface area provides sufficient active reactionsites needed to keep up with the cathode reaction at high dischargerates. Accordingly, it is desirable to provide cells having apredetermined amount of anode active material particles, which in someembodiments are in the form of zinc or a zinc alloy. The concentrationof anode active material in the anode may vary for a given application,and/or electrochemical cell configuration. Typically, however, the totalamount of anode active material present in the anode, or more generallythe amount of anode active material, is at least about 50 wt %, about 60wt %, about 70 wt %, or about 80 wt %, the concentration for examplebeing between about 50 wt % and about 80 wt %, between about 55 wt % andabout 75 wt %, or between about 60 wt % and about 70 wt % (e.g., about64 wt %, about 66 wt %, or about 68 wt %), based on the total weight ofthe anode. Thus, in some embodiments, the anode active material ispresent in the gelled anode mixture at a concentration of from about 55%to about 75% by weight, based on the total weight of the gelled anodemixture.

As noted herein, this anode active material may have a range of particlesizes, and/or particle size distributions. For example, the anode maycomprise anode active material particles having a particle size of lessthan about 75 microns (−200 mesh size), which may be referred to hereinas “fines.” In particular, anode active material particles that passthrough a 200 mesh screen size, and thus have a particle size of lessthan about 75 microns, may be present in the anode in an amount of, forexample, less than about 10 wt % or about 5 wt %, relative to the totalzinc in the anode (including coarse zinc particles, or zinc particleshaving a particle size of greater than about 75 microns), and in someembodiments may be present in the anode in an amount of between about 1wt % and about 10 wt %, or between about 2 wt % and about 8 wt %, orbetween about 3 wt % and about 6 wt %.

It is to be noted that mesh sizes are stated herein to specify a rangeof particle sizes. For example, “−200 mesh” generally indicatesparticles smaller than about 75 microns, while “+200 mesh” generallyindicates particles larger than about 75 microns.

It is to be further noted that, additionally or alternatively, desirableresults may also be achieved using an amount of anode active materialfines (e.g., zinc) greater than about 10 wt % (e.g., about 150, about 20wt %, about 30 wt %, about 40 wt %, or even about 50 wt %), based on thetotal weight of anode active material present in the anode. The use offines may be particularly useful when, for example, the particle size ofthe other active material particles (i.e., coarse zinc particles) beingused is, for example, between about 75 and about 105 microns (+75 and−140 mesh size). These coarse particles may be present in an amountbetween, for example, about 1 wt % and about 50 wt %, or between about10 wt % and about 40 wt %, based on the total weight of anode activematerial present in the anode.

It is to be still further noted that multiple ranges of anode activematerial particles having a diameter less than about 105 microns (−140mesh size), including particles between about 75 and about 105 microns(+200 and −140 mesh size) and fines less than about 75 microns (−200mesh size), may be used to increase cell performance. For instance, theanode may include active material particles between about 75 and about105 micrometers, with the advantages in cell performance being enhancedwhen the anode gel has a low electrolyte concentration, as detailedelsewhere herein. When fines have a size between the range of about 20and about 75 micrometers (+625 and −200 mesh size), or alternativelybetween about 38 and about 75 micrometers (+400 and −200 mesh size),cell performance may be particularly enhanced when the electrolyteconcentration is low, as detailed elsewhere herein.

In some embodiments of the present disclosure, from about 5% to about35%, by weight of the total anode active material present in the gelledanode mixture have a particle size of less than about 75 microns. Inother embodiments, from about 10% to about 25%, by weight, of the totalanode active material present in the gelled anode mixture have aparticle size of less than about 75 microns. In yet other embodiments,greater than about 10%, by weight, of the total anode active materialpresent in the gelled anode mixture have a particle size of less thanabout 45 microns. In other embodiments of the present disclosure, fromabout 8% to about 35%, by weight, of the anode active material presentin the gelled anode mixture have a particle size of less than about 75microns. In yet other embodiments, from about 10% to about 21%, byweight, of the anode active material present in the gelled anode mixturehave a particle size of less than about 75 microns.

2. Apparent Density/Aspect Ratio

In the electrochemical cells of the present disclosure, the anode activematerial has an apparent density that leads to cell performanceimprovements compared to those of the prior art. The apparent density ofthe anode active material is an important characteristic of the presentdisclosure. Specifically, for example, reducing the apparent density ofthe anode active material below conventional levels enhances the anodedischarge efficiency at high drains of discharge. High rate dischargeperformance is dependent on the availability of sufficient anodereaction sites in the vicinity of the anode-cathode interface. Though,in some instances, this may be accomplished by increasing the level ofanode active material fine particles, increasing the level of fines hasa limit to improving performance because the discharge product aroundthe fine particles disrupts particle-to-particle contact and also tendsto suppress ion diffusion, which can be an essential step to sustainfast anode/cathode reactions demanded by high drain rates. In accordancewith the present disclosure, anode reaction sites can be increased, andthus high rate discharge of the cells enhanced, by enlarging the anodesurface area through the use of low apparent density anode activematerial.

Apparent density is the weight per unit volume of a given material(e.g., anode active material). The apparent density may be measured, forexample, by ASTM B212-13, Standard Test Method for Apparent Density ofFree-Flowing Metal Powders Using the Hall Flowmeter Funnel.

Further, proper control of the anode active material apparent densityaccording to the present disclosure increases the anode reaction sitesin the vicinity of the anode-cathode interface. Within the cell, thereaction progresses from the anode-cathode interface towards the corecentral part of the anode and from the cathode-anode interface towardsthe can-cathode interface in cylindrical cells. As the reactionprogresses, oxidized anode active material product (e.g., zinc oxide)forms and the electrolyte is rapidly consumed forming a dry dischargeproduct that tends to impair diffusion of reactants toward the anodecore and/or toward the can-cathode interface.

High drain discharge of cells can be accomplished by performing theDigital Still Camera (DSC) test, which is generally known in the art ofelectrochemical cells. The DSC test applies a pulse load of 1500 mW for2 seconds followed by 650 mW for 28 seconds for 5 minutes every houruntil the cell closed circuit voltage reaches 1.05 V. Another exemplaryhigh drain test known in the industry is a Photo Pulse test, whichapplies 1 Amp of load for 10 seconds each minute for one hour dailyuntil the cell closed circuit voltage reaches 0.9 V.

In accordance with the present disclosure, electrochemical cellperformance, as well as DSC performance, is improved by adjusting theapparent density of the anode active material. Specifically, in someembodiments of the present disclosure the anode active material apparentdensity is adjusted to levels below 3.00 grams/cubic centimeter (g/cc).In some embodiments of the present disclosure, the anode active materialapparent density is decreased by progressively increasing the percentageof small and relatively large elongated anode active material particles.It has been surprisingly found by the present disclosure that elongatedanode active material particles improve packing, enhanceparticle-to-particle contact, and increase active anode reaction sitesthat are necessary for high drain capability.

Accordingly, in some embodiments of the present disclosure, the anodeactive material has an apparent density below about 3.00 g/cc. In otherembodiments, the anode active material has an apparent density of fromabout 2.55 g/cc to about 2.95 g/cc, in some embodiments from about 2.65g/cc to about 2.85 g/cc, in some embodiments about 2.95 g/cc, in someembodiments about 2.85 g/cc, and in some embodiments about 2.70 g/cc. Inyet other embodiments, the anode active material has an apparent densityof about 2.71 g/cc; in some embodiments about 2.83 g/cc; and in someembodiments about 2.94 g/cc. In still other embodiments, the anodeactive material has an average apparent density of about 2.70 g/cc; inother embodiments an average apparent density of about 2.80 g/cc; and inyet other embodiments an average apparent density of about 2.95 g/cc.

In order to achieve a low apparent density of the anode active material,in some embodiments of the present disclosure, the level of elongatedanode active material particles is increased. The aspect ratio of theanode active material can be quantified by the length of an anode activematerial particle divided by the thinnest width of an anode activematerial particle. Specifically, the level or fraction of elongatedanode active material particles with an aspect ratio greater than 10.0is increased. In some embodiments, this fraction of anode activematerial elongated particles can have aspect ratios of from about 10.0to about 50.0, and in some embodiments can be from about 15.0 to about30.0. In other embodiments, said aspect ratio may be from about 10.0 toabout 40.0. In yet still other embodiments, the aspect ratio may be fromabout 30.0 to about 50.0. Thus, the anode active material in accordancewith the present disclosure can comprise particles having an aspectratio of from about 10.0 to about 50.0, from about 10.0 to about 40.0,from about 15.0 to about 30.0, and/or from about 30.0 to about 50.0.

The larger the amount of elongated anode active material particles inthe anode active material, the higher the fraction of particles withhigh aspect ratio and the lower the apparent density of the anode activematerial. For example, in some embodiments of the present disclosure, asdisclosed in FIG. 9, the anode active material will contain particlesthat are from about 800 microns to about 1000 microns long and fromabout 20 microns to about 25 microns wide, for an aspect ratio of from30.0 to about 50.0.

Moreover, as can be seen in the comparison of FIG. 8A and FIG. 8B, whenthe anode active material apparent density is less than 3.0 g/cc (i.e.,2.71 g/cc in FIG. 8A), the fraction of elongated particles with anaspect ratio greater than 10.0 is larger than that exhibited by a powderwith an apparent density of 3.04 g/cc (FIG. 8B). As can be seen in thefigures, this is due to the amount of more elongated particles in FIG.8A, which in turn produces a lower apparent density material.

Further, examples of anode active material powders with relatively largeelongated particles according to this disclosure can also be seen inFIGS. 7A and 7B. FIG. 7A shows the particle size distribution of a zincalloy comprising 120 ppm of bismuth and 120 ppm of indium with anapparent density of 2.71 g/cc. FIG. 7B shows the particle sizedistribution of a zinc alloy comprising 120 ppm of bismuth and 120 ppmof indium with an apparent density of 2.95 g/cc.

3. Electrolyte

With respect to the type and concentration of the electrolyte in thegelled anode, as previously noted, the gelled anode of the presentdisclosure includes an alkaline electrolyte, and in some embodiments analkaline electrolyte having a relatively low hydroxide content. Suitablealkaline electrolytes include, for example, aqueous solutions ofpotassium hydroxide, sodium hydroxide, lithium hydroxide, as well ascombinations thereof. In one particular embodiment, however, a potassiumhydroxide-containing electrolyte is used. In other embodiments, thealkaline electrolyte comprises water and potassium hydroxide.

Also, as previously noted, electrolytes utilized in accordance with thepresent disclosure typically have a hydroxide (e.g., potassiumhydroxide) concentration of about 35%, about 30% or less (e.g., about29%, about 28%, about 27%, about 26%, or even about 25%), based on thetotal electrolyte weight. However, typically the electrolyte has ahydroxide concentration of between about 25% and about 35%, or betweenabout 26% and about 30%. In one particular embodiment (e.g., a gelledanode suitable for use in a cell sized and shaped as, for example, an AAor AAA cell), the hydroxide concentration of the electrolyte is about28% by weight, based on the total weight of the electrolyte.

In this regard it is to be noted that the concentration of therelatively low hydroxide content electrolyte in the gelled anode isgenerally at or near that of conventional gelled anodes, theconcentration for example typically being at least about 24% by weight,at least about 26% by weight, or at least about 28% by weight, and lessthan about 34% by weight, less than about 32% by weight, or less thanabout 30% by weight, based on the total weight of the gelled anode. Theconcentration of the electrolyte in gelled anodes of the presentdisclosure may, therefore, typically be within the range of from about24% by weight to about 34% by weight, from about 26% by weight to about32% by weight, or from about 28% by weight to about 30% by weight, basedon the total weight of the gelled anode. The desired concentration ofelectrolyte in the gelled anode generally depends on a variety offactors including, for example, the concentration of zinc in the gelledanode.

B. Gelling Agent

Without being held to any particular theory, it is generally believedthat one or more characteristics of the gelling agent (e.g., the densityor viscosity thereof) utilized in accordance with the present disclosurecontribute, at least in part, to its suitability for use in a gelledanode, particularly one having a relatively low potassium hydroxidecontent. More specifically, it is generally believed that the highlycrosslinked gelling agent imparts a rigid-type gel structure and aslightly decreased packing density to the gelled anode within the cell,as well as a corresponding greater but more stable anodeparticle-to-particle distance than provided by conventional gellingagents. These features of the anode gels are believed to contribute toimproved reactant transport and wettability throughout the anode gel,enhancing cell discharge performance. In particular, the gelled anode ofthe present disclosure is believed to contribute to improved transportof hydroxyl ions throughout the anode mass during cell discharge, whichis generally preferred under certain conditions including, for example,high rate intermittent or continuous discharge. As further detailedelsewhere herein, various features of the gelling agent may beindicators of the suitability of these gelling agents for use in agelled anode having relatively low potassium hydroxide content,including for example the degree of crosslinking in the gelling agent,and/or the viscosity and/or density thereof.

Generally speaking, the gelling agent of the present disclosure is ahighly crosslinked, polymeric chemical compound that has negativelycharged acid groups. The function of these acid groups is to expand thepolymer backbone into an entangled matrix. When these acid groups areionized in the anode, they repel each other and the polymer matrixswells to provide a support mechanism. One gelling agent particularlywell-suited for use in accordance with the present disclosure is apolyacrylic acid gelling agent having a high degree of crosslinkingtherein, or a degree of crosslinking which is greater than that presentin conventionally employed gelling agents (such as for example thosecommercially available under the name Carbopol™). In particular, morehighly crosslinked polyacrylic acid gelling agents, commerciallyavailable under the name Flogel™ (e.g., Flogel™ 700 or 800) from SNFHolding Company (Riceboro, Ga.), are suitable for use in accordance withthe present disclosure.

In addition to the increased degree of crosslinking present in thegelling agent (as compared, for example, to those commercially availableunder the name Carbopol™), additional advantageous features of thegelling agent are its viscosity and/or density. Generally speaking, theviscosity and/or the density of the gelling agent utilized in thepresent disclosure is/are greater than that of conventionally employedgelling agents. For example, the viscosity of suitable gelling agents atabout 25° C. is generally at least about 40,000 centipoise (cp), atleast about 45,000 cp, at least about 50,000 cp, or at least about55,000 cp. In accordance with certain embodiments of the presentdisclosure, however, the viscosity of suitable gelling agents is atleast about 58,000 cp, about 60,000 cp, about 62,000 cp, about 64,000cp, about 66,000 cp, about 68,000 cp, or even about 70,000 cp.Accordingly, the viscosity of suitable gelling agents may generallyrange, for example, from about 50,000 cp to about 70,000 cp, from about60,000 cp to about 68,000 cp, or from about 62,000 cp to about 66,000cp, at about 25° C.

As previously noted, the viscosities of gelling agents reported hereinare with reference to the viscosity of a 0.5 wt. % aqueous solution ofthe gelling agent and may be measured using means conventionally knownin the art including, for example, using a viscometer commerciallyavailable from Brookfield Engineering Laboratories, Inc. (Middleboro,Mass.) under standard conditions. For example, a RVT Brookfieldviscometer having a No. 5 spindle and operated at 1 revolution perminute (rpm) may be used to measure the viscosity of aqueous solutionscontaining gelling agents of the present disclosure. This and othersuitable apparatus may also be used to measure the viscosity of gelledanodes of the present disclosure.

With respect to the bulk density of suitable gelling agents (i.e., thedensity of the gelling agent in powder form), it is to be noted thatthis is generally at least 0.21 grams/cubic centimeter (g/cc), and maybe at least 0.22 g/cc, at least 0.23 g/cc, at least 0.24 g/cc, at least0.25 g/cc or more (e.g., about 0.26, 0.28, 0.3 or more g/cc). Typically,however, the density of suitable gelling agents is from 0.22 g/cc toabout 0.3 g/cc, or from 0.24 g/cc to about 0.28 g/cc. In this regard itis to be noted that the bulk density of gelling agents of the presentdisclosure may be determined using means and apparatus known in the artincluding, for example, the method described in ASTM C29/C29M-97 (2003),but generally are determined by measuring the mass of a predeterminedvolume of the gelling agent. The bulk density of gelled anodes of thepresent disclosure may generally be determined in the same or a similarmanner.

The concentration of the gelling agent in the anode, and morespecifically the gelled anode, may be optimized for a given use.Typically, however, the concentration of the gelling agent in the gelledanode is at least about 0.40 weight %, based on the total weight of thegelled anode, and may be at least about 0.50 weight %, at least about0.55 weight %, at least about 0.6 weight %, at least about 0.625 weight%, at least about 0.65 weight %, at least about 0.675 weight %, at leastabout 0.7 weight % or more. For example, in various embodiments theconcentration of the gelling agent in the gelled anode may be from about0.40% to about 0.75%, or between about 0.50% and 0.75%, or between about0.6% and about 0.7%, or between about 0.625% and about 0.675%, by weightof the gelled anode. In one particular embodiment, the concentration isabout 0.60 weight % (when for example it is used in combination with anabsorbent as a gelled anode component), while in another embodiment theconcentration is between about 0.62 and about 0.66 weight % (when forexample it is used without an absorbent as a gelled anode component).

In addition to the degree of crosslinking, the viscosity and/or density,the gelling agent of the present disclosure may also be characterized bythe flow properties (e.g., viscosity) and/or the density of the gelledanode of which it is a part. For example, with respect to the flowproperties of the gelled anode, it is to be noted that, in addition toincreased viscosity of the gelling agent of the present disclosure (ascompared to a conventional gelling agent), the viscosity of freshly-madegelled anodes of the present disclosure containing such an agent may, inat least some embodiments, typically be greater than that of afreshly-made, conventional gelled anode. Generally, the initialviscosity of freshly-made gelled anodes of the present disclosure at 25°C. is at least about 60,000 cp, at least about 80,000 cp, or at leastabout 100,000 cp. More particularly, the initial viscosity offreshly-made gelled anodes of the present disclosure at 25° C. istypically at least about 120,000 cp, at least about 160,000 cp, at leastabout 180,000 cp, at least about 200,000 cp, at least about 240,000 cp,at least about 280,000 cp, or at least about 300,000 cp. For example,the initial viscosity of a gelled anode of the present disclosure at 25°C. may be in the range of from about 120,000 cp to about 360,000 cp,from about 160,000 cp to about 320,000 cp, from about 180,000 cp toabout 300,000 cp, from about 200,000 cp to about 280,000 cp, or fromabout 220,000 cp to about 260,000 cp.

In this regard, it is noted that “initial” viscosity of a freshly-madegelled anode refers to viscosity of the gelled anode determined beforestorage of the anode for any significant period of time. In particular,initial viscosity refers to the viscosity of the gelled anode determinedwithin about 15 minutes of its preparation, within about 30 minutes ofits preparation, within about 45 minutes of its preparation, or withinabout 60 minutes of its preparation.

As a result of the viscosity of the gelling agent of the presentdisclosure, an anode gel prepared using this gelling agent is typicallymore rigid than a gel prepared using a conventional gelling agent,particularly after being stored for a period of time. For example, usingmeans known in the art, it may be observed that a conventionallyprepared anode gel (e.g., one prepared using a similar amount of, forexample, a Carbopol™ agent, such as Carbopol™ 940) may exhibit aninitial viscosity (i.e., a viscosity measured immediately afterpreparation) similar to the initial viscosity of the gelled anode of thepresent disclosure. In contrast, however, while the conventionallyprepared gelled anode may exhibit little change in viscosity afterhaving been prepared and stored at room temperature (e.g., about 20-25°C.) for a period of time, the gelled anode of the present disclosuremay, after having been stored at about room temperature for essentiallythe same period of time (e.g., at least about 8 hours, about 12 hours,about 18 hours or even about 24 hours), exhibits a viscosity that hasincreased, relative to the initial viscosity, by at least about 20%, atleast about 30%, at least about 40%, at least about 50%, at least about60%, at least about 70%, or at least about 80%. For example, in variousembodiments, the viscosity of the gelled anode of the present disclosuremay increase after storage by from about 20% to about 80%, from about30% to about 70%, from about 40% to about 60%, or from about 45% toabout 55%.

It is to be further noted that, in accordance with the above descriptionof initial viscosities of gelled anodes of the present disclosure, andviscosities after storage, it has been observed that before and/or afterincorporation into an electrochemical cell, gelled anodes of the presentdisclosure generally exhibit a viscosity of at least about 125,000 cp,at least about 150,000 cp, at least about 200,000 cp, at least about225,000 cp, at least about 250,000 cp, at least about 275,000 cp, atleast about 300,000 cp, at least about 325,000 cp, at least about350,000 cp, at least about 375,000 cp, at least about 400,000 cp, atleast about 410,000 cp, at least about 420,000 cp, or more. Typically,however, gelled anodes of the present disclosure exhibit a viscosity ofbetween at least about 125,000 cp and less than 500,000 cp, of fromabout 175,000 cp to about 450,000 cp, from about 300,000 cp to about425,000 cp, from about 325,000 cp to about 400,000 cp, from about340,000 cp to about 390,000 cp, or from about 350,000 cp to about375,000 cp.

It is to be noted that viscosities and densities of the gelled anodereported herein may be determined using conventional means known in theart (including, for example, the apparatus described above for use inmeasuring the viscosity of gelling agents of the present disclosure).

C. Additional Anode Components

A gelled anode of the present disclosure may also employ othercomponents or additives, in addition to the gelling agent and the anodeactive material and the electrolyte. For example, in one particularembodiment, an absorbent (e.g., superabsorbent) is employed. Withoutbeing held to any particular theory, it is generally believed that thesematerials generally absorb and retain water in the gelled anode andallow electrolyte to be retained near the anode active material (e.g.,zinc); that is, the absorbent is believed to function as an electrolytereservoir. It is also believed that absorbent material promotes contactbetween anode active material particles and promotes formation of agelled anode in which these particles are in better electrical contact.When an absorbent material is present in the gelled anode, any or all ofthese features of the absorbent material are believed to enhance theperformance of the gelled anode.

Suitable absorbent materials may be selected from those generally knownin the art. Exemplary absorbent materials include those sold under thetrade name Salsorb™ or Alcasorb™ (e.g., Alcasorb™ CL15), which arecommercially available from Ciba Specialty (Carol Stream, Ill.), oralternatively those sold under the trade name Sunfresh™ (e.g., SunfreshDK200VB), commercially available from Sanyo Chemical Industries (Japan).

Advantageously, the gelling agent of the present disclosure enables areduced amount (e.g., about 30%, about 50% or even about 70% less) of anabsorbent to be used to prepare a gelled anode, as compared for exampleto a conventional gelled anode and a gelling agent, to thereby reducethe cost of the gelled anode. For example, generally the concentrationof absorbent in gelled anodes of the present disclosure is less thanabout 0.2%, less than about 0.15%, less than about 0.125%, less thanabout 0.1%, less than about 0.075%, less than about 0.05%, less thanabout 0.025%, or even less than about 0.01%, of the total anode weight.Typically, however, the concentration of absorbent in the gelled anodeof the present disclosure is from about 0.01% to about 0.2% by weight,from about 0.025% to about 0.15% by weight, or from about 0.05% to about0.1% by weight. For example, in various embodiments the gelled anode maycomprise 0.04 wt %, or about 0.05 wt %, or about 0.06 wt %, of anabsorbent material.

As a result of the reduced concentration of absorbent, and/or theincreased concentration of gelling agent, present in the gelled anode ofthe present disclosure, the weight ratio of the gelling agent toabsorbent therein is generally greater than that associated withconventional gelled anodes. For example, in various embodiments theratio of gelling agent to absorbent may be at least 3:1, at least about3.5:1, at least about 4:1, at least about 5:1, at least about 7.5:1, atleast about 10:1, or at least about 12.5:1. Typically, the ratio ofgelling agent to absorbent is from at least 3:1 to about 25:1, fromabout 4:1 to about 22.5:1, from about 5:1 to about 20:1, from about7.5:1 to about 17.5:1, or from about 10:1 to about 15:1.

In this regard it is to be noted that the concentration of the gellingagent and/or the absorbent may be adjusted for a given use, as afunction of for example the electrolyte (e.g., potassium hydroxide)and/or zinc concentration, the desired flow properties (e.g., viscosity)and/or density.

In particular, it is to be noted that the concentration of the gellingagent in the gelled anode, the concentration of absorbent in the gelledanode, and the relative proportion of these two components of the gelledanode, may be inter-related and thus work in combination to affect theviscosity of the gelling agent. Accordingly, among the variousembodiments of the present disclosure, the following exemplarycombinations may be noted: (i) when the viscosity of the gelled anode isbetween at least about 300,000 cp and less than about 500,000 cp, theconcentration of the gelling agent in the anode may typically be fromabout 0.40% to about 0.75%, the concentration of the absorbent in thegelled anode may typically be from about 0.01% to about 0.2% by weight,and/or the weight ratio of the gelling agent to the absorbent maytypically be from 3:1 to about 25:1; (ii) when the viscosity of thegelled anode is between about 310,000 cp to about 475,000 cp, theconcentration of the gelling agent in the gelled anode may typically befrom about 0.40% to about 0.75%, the concentration of the absorbent inthe gelled anode may typically be from about 0.01% to about 0.2% byweight, and/or the weight ratio of the gelling agent to absorbent maytypically be from about 4:1 to about 22.5:1; (iii) when the viscosity ofthe gelled anode is from about 320,000 cp to about 450,000 cp, theconcentration of the gelling agent in the gelled anode may typically bebetween about 0.50% and 0.75%, the concentration of the absorbent in thegelled anode may typically be from about 0.01% to about 0.2% by weight,and/or the weight ratio of the gelling agent to the absorbent maytypically be from about 5:1 to about 20:1; (iv) when the viscosity ofthe gelled anode is from about 330,000 cp to about 425,000 cp, theconcentration of the gelling agent in the gelled anode may typically bebetween about 0.6% and about 0.7%, the concentration of the absorbent inthe gelled anode may typically be from about 0.025% to about 0.15% byweight, and/or the weight ratio of the gelling agent to the absorbentmay typically be from about 7.5:1 to about 17.5:1; and/or (v) when theviscosity of the gelled anode is from about 340,000 cp to about 400,000cp, the concentration of the gelling agent in the gelled anode maytypically be between about 0.625% and about 0.675%, the concentration ofthe absorbent in the gelled anode may typically be from about 0.05% toabout 0.1% by weight, and/or the weight ratio of the gelling agent tothe absorbent may typically be from about 10:1 to about 15:1.

In addition to an absorbent material, the gelled anode may additionallyor alternatively comprise a gassing inhibitor (e.g., organic inhibitor).In some embodiments of the present disclosure, the gassing inhibitor isa phosphate ester. In other embodiments, the gassing inhibitor is anorganic phosphate ester. Suitable corrosion or gassing inhibitorsinclude, for example, RHODAFAC® RM-510 and RHODAFAC® RS-610, which arecommercially available from Rhodia (Boston, Mass.).

When used, the amount of gassing inhibitor present in the gelled anodemay be determined or selected to optimize performance of the anode.Typically, however, the concentration of the inhibitor in the gelledanode will be at least about 10 ppm, about 25 ppm, about 50 ppm, about100 ppm, about 150 ppm, about 200 ppm or more. In some embodiments, theconcentration is in the range of about 10 ppm to about 150 ppm, or about25 ppm to about 50 ppm, when for example a phosphate-type corrosion orgassing inhibitor is used. In some embodiments, the concentration of theinhibitor in the gelled anode mixture is about 35 ppm.

D. Electrolyte Preparation

The electrolyte may be prepared using methods generally known in theart. In accordance with the present disclosure, this preparation may forexample involve forming an aqueous solution of a metal hydroxide salt,such as potassium, lithium or sodium hydroxide, and optionally a portionof the gelling agent (as detailed elsewhere herein). The electrolytesolution itself may comprise, for example, from about 20% to about 50%,and desirably from about 25% to about 40% of a hydroxide salt (e.g.,potassium hydroxide), based on the total weight of the electrolyte.

The electrolyte fabrication process may include adding zinc oxide to theelectrolyte solution, for example to reduce dendrite growth, which inturn reduces the potential for internal short circuits by reducing thepotential for separator puncturing. Although in at least some of theembodiments described herein, the zinc oxide need not be provided in theelectrolyte solution, as an equilibrium quantity of zinc oxide isultimately self-generated in situ over time by the exposure of zinc tothe alkaline environment and the operating conditions inside the cell,with or without the addition of zinc oxide per se. The zinc used informing the zinc oxide is drawn from the zinc already in the cell, andthe hydroxide is drawn from the hydroxyl ions already in the cell. Wherezinc oxide is added to the electrolyte solution, the zinc oxide istypically present in an amount of from about 0.5% to about 4%, or about1% to about 2%, based on the weight of the electrolyte solution, and mayin some embodiments be about 2% by weight.

As previously noted, the gelled anodes of the present disclosure mayalso employ an absorbent (i.e., superabsorbent), and in at least someembodiments typically employ such an absorbent.

III. Cathode

In accordance with one or more embodiments of the present disclosure, acathode suitable for use in an alkaline electrochemical cell as detailedherein may comprise at least one cathode active material. Other optionalcomponents, such as a binder, may be present in the cathode mixture, aswell. The cathode active material may be amorphous or crystalline, or amixture of amorphous and crystalline, and may be essentially anymaterial generally recognized in the art for use in alkalineelectrochemical cells. For example, the cathode active material maycomprise, or be selected from, an oxide of copper, an oxide of manganeseas electrolytic, chemical, or natural type (e.g., EMD, CMD, NMD, or amixture of two or more thereof), an oxide of silver, and/or an oxide orhydroxide of nickel, as well as a mixture of two or more of these oxidesor hydroxide. Suitable examples of positive electrode materials include,but are not limited to, MnO₂ (EMD, CMD, NMD, and mixtures thereof), NiO,NiOOH, Cu(OH)₂, cobalt oxide, PbO₂, AgO, Ag₂O, Ag₂Cu₂O₃, CuAgO₂, CuMnO₂,CuMn₂O₄, Cu₂MnO₄, Cu_(3-x)Mn_(x)O₃, Cu_(1-x)Mn_(x)O₂, Cu_(2-x)Mn_(x)O₂(where x<2), Cu_(3-x)Mn_(x)O₄ (where x<3), Cu₂Ag₂O₄ and suitablecombinations thereof.

In at least one embodiment of the present disclosure, the cathodemixture comprises an oxide of copper. In this regard it is to be notedthat, as used herein, the term “copper oxide” is intended to refer tocupric oxide, where the copper has an oxidation state of about +2.

Conventional cathodes may typically include a binder. In thoseembodiments wherein a conventional binder is employed, it is typicallyin powder or particulate form. Generally, any conventional bindersuitable for use in a cathode in an alkaline electrochemical cell may beused, provided it is suitably compatible with the other componentstherein. Such binders may include, for example, polyethylene binders(e.g., (i) low density PE, such as low density PE grade 1681-1,commercially from DuPont, (ii) high density PE, (iii) a mixture of lowand high density PE), polyvinyl alcohol binders, as well as mixtures ofone or more thereof.

In general, the type and concentration of the cathode active material,or materials when a mixture is used, as well as the type andconcentration of the other components that may optionally be present inthe cathode, will be selected in order to optimize the overallperformance of the electrochemical cell of which the cathode is a part.Typically, however, the concentration of the active material, or totalconcentration of active materials when a mixture is used, may be betweenabout 70 wt % and less than about 100 wt %, based on the total weight ofthe cathode, and may be between about 75 wt % and about 95 wt %, orabout 80 wt % and about 90 wt %, of the total cathode weight. Forexample, in various embodiments the concentration of the cathode activematerial may be about 70 wt %, about 80 wt %, or about 90 wt %, based onthe total weight of the cathode.

IV. Separator

Generally any separator material and/or configuration suitable for usein an alkaline electrochemical cell, and with the cathode and/or anodematerials set forth herein above, may be used in accordance with thepresent disclosure. More particularly, one embodiment of the presentdisclosure includes a sealed separator system for an electrochemicalcell that is disposed between a gelled anode of the type described hereand a cathode containing soluble species of for example copper, silver,or both, as described above.

In this regard it is to be noted that the term “sealed separator system”is used herein to define a structure that physically separates the cellanode from the cathode, enables hydroxyl ions and water to transferbetween the anode and cathode, limits transport other than through thematerial itself by virtue of a seam and bottom seal, and effectivelylimits the migration through the separator of some soluble species suchas copper, silver, nickel, iodate, bismuth and sulfur species from thecathode to the anode. The choice of separator material and the need fora “sealed separator system” may depend, to some extent, upon the cathodeactive material in the cell, and whether or not anode-fouling speciesare produced. In a conventional alkaline cell using a manganese dioxidecathode where no significant anode fouling species are produced (otherthan those from minor trace impurities present), a film separator suchas one made of polyvinyl alcohol or cellophane alone, in combinationwith each other, or in combination with a non-woven material may be usedwithout a bottom or side seam seal so long as adequate measures aretaken to prevent internal soft shorting by transport of fineparticulates along or past the unsealed areas. The use of an adhesive,may optionally be used to effectively limit the crossover between theanode and cathode compartments over the top of the separator, by bondingor sealing the separator with the sealing assembly and/or container ofthe electrochemical cell, to effectively minimize physical and/orchemical transport between the anode and the cathode compartments of thecell.

It is to be noted that, in one alternative embodiment, the presentdisclosure is directed generally to a conventional alkalineelectrochemical cell, or alternatively to an alkaline electrochemicalcell which comprises one or more components that may form an anodefouling species in the cell, which comprises a thin film separator.

V. Cell Types

It should be understood that the gelled anodes of the present disclosuremay be added to essentially any anode in any type of electrochemicalcell including, but not limited to, zinc-manganese dioxide cells,zinc-silver oxide cells, metal-air cells including zinc in the anode,nickel-zinc cells, rechargeable zinc/alkaline/manganese dioxide (RAM)cells, zinc-copper oxide cells, or any other cell having a zinc-basedanode. It should also be appreciated that the present disclosure isapplicable to any suitable button-type cell, and/or any suitablecylindrical metal-air cell, such as those sized and shaped, for example,as AA, AAA, AAAA, C, and D cells.

VI. Cell Performance

As further detailed elsewhere herein, the electrochemical cells of thepresent disclosure have been observed to exhibit improved performancecharacteristics, which may be measured or tested in accordance withseveral methods under the American National Standards Institute (ANSI).Results of various tests of cells of the present disclosure are detailedbelow in the Examples.

The following Examples describe various embodiments of the presentdisclosure. Other embodiments within the scope of the appended claimswill be apparent to a skilled artisan considering the specification orpractice of the disclosure provided herein. It is therefore intendedthat the specification, together with the Examples, be consideredexemplary only, with the scope and spirit of the disclosure beingindicated by the claims, which follow the Examples.

EXAMPLES

In the Examples presented below, electrochemical cells of the presentdisclosure were tested for DSC performance, drop test amperage (bothbefore and after the drop), partial discharge gassing and conditionsafter storage.

Example 1 DSC Performance with Alloys Containing Fines

Gelled anodes were prepared in accordance with the improvements of thepresent disclosure. FIG. 2 displays the mean DSC pulse performance ofLR6 cells made at three gassing inhibitor conditions with two differentzinc alloys as the anode active material. The gassing inhibitors testedwere RHODAFAC® RM-510 (A-35 ppm) and RHODAFAC® RS-610 (B-35 ppm and B-50ppm). The two zinc alloys tested included 120 ppm of both bismuth andindium and 200 ppm of both bismuth and indium. The zinc apparent densityvalues in FIG. 2 indicated as 2.70, 2.80 and 2.95 g/ml correspond to theaverage apparent density of the two alloys at about 2.71, 2.83 and 2.94g/cc. The zinc alloys contained about 15%, by weight, of fine particles(i.e., particles having a size of about 75 microns or less).

As noted above, the three different apparent densities tested averaged2.94 g/cc, 2.83 g/cc and 2.71 g/cc. As can be seen in FIG. 2,independent of the type of alloy and gassing inhibitor content, the DSCperformance increased with decreased apparent density of the anodeactive material.

Example 2 Cell Amperage after Drop Test

Cells prepared in accordance with the specifications of Example 1 (i.e.,same apparent densities, zinc alloys, fine %, gassing inhibitor content,etc.) were tested for their cell amperage after a drop test.

Prior to the drop test, cell amperage of each cell was taken. Onceagain, as can be seen in FIG. 4 (which displays the mean cell amperage),cells with the lower apparent density had the higher cell amperage. Thisis in accord with the expectation of increased particle-to-particlecontact with decreased apparent density. The zinc apparent densityvalues in FIG. 4 indicated as 2.70, 2.80 and 2.95 g/ml correspond to theaverage apparent density of the two alloys at about 2.71, 2.83 and 2.94g/cc.

For the drop test, the flash amps and open circuit voltage (OCV) of 15AA batteries were recorded. Each battery was then rolled off of a flatsurface 5 times from a height of about 102 cm onto a vinyl coveredfloor. The batteries were then allowed to rest for one hour. Then, thefinal flash amp and OCV readings were taken. In order to pass the droptest, the individual OCV readings may not decrease more than 20 mV, theaverage final amp results must be at least 70% of the initial averageamp results, and all individual batteries must have at least a final ampvalue of 3.0 A. The amperage is checked again on each qualifying batteryand the “post drop” amperage is compared to the initial amperage. Theresults are presented in FIG. 3 as the percentage of the initialamperage.

The zinc apparent density values in FIG. 3 indicated as 2.70, 2.80 and2.95 g/ml correspond to the average apparent density of the two alloysat about 2.71, 2.83 and 2.94 g/cc. As can be seen in FIG. 3, the cellswith the lower apparent density have the highest percentage of cellamperage after being dropped.

Example 3 Partial Discharge Gassing of Cells

Cells prepared in accordance with the specifications of Example 1 (i.e.,same apparent densities, zinc alloys, fine %, gassing inhibitor content,etc.) were tested for partial discharge gassing. The zinc apparentdensity values in FIG. 5 indicated as 2.70, 2.80 and 2.95 g/mlcorrespond to the average apparent density of the two alloys at about2.71, 2.83 and 2.94 g/cc.

A potentially adverse effect of lowering the anode active materialapparent density is a tendency of increased partial discharge cellgassing, which can be seen in FIG. 5 (which displays the mean cellgassing in ml of volume). An appropriate gassing inhibitor andappropriate concentration amounts can be used to suppress cell gassing,however, as seen in FIG. 5 with additions of RHODAFAC® RM-510 orRHODAFAC® RS-610 inhibitors.

Example 4 DSC Performance of Cells after Storage

Two groups of cells were tested for their DSC performance after 3 monthsof storage. The first group of cells included a zinc alloy comprising200 ppm of bismuth and 200 ppm of indium as the anode active materialand had an apparent density of 2.94 g/cc. The second group of cellsincluded a zinc alloy comprising 120 ppm of bismuth and 120 ppm ofindium as the anode active material and had an apparent density of 3.04g/cc. Each group of cells included about 15% of fine particles in theanode active material.

Both groups of cells were tested for DSC performance after 3 months ofstorage and with different gassing inhibitor levels (i.e., 35 ppm of agassing inhibitor and 46 ppm of a gassing inhibitor). As can be seen inFIG. 6, at both gassing inhibitor levels the cells having the lower zincalloy apparent density exhibited an improved performance over the cellshaving an apparent density over 3.00 g/cc.

When introducing elements of the present disclosure or the variousversions, embodiment(s) or aspects thereof, the articles “a”, “an”,“the” and “said” are intended to mean that there are one or more of theelements. The terms “comprising”, “including” and “having” are intendedto be inclusive and mean that there may be additional elements otherthan the listed elements. The use of terms indicating a particularorientation (e.g., “top”, “bottom”, “side”, etc.) is for convenience ofdescription and does not require any particular orientation of the itemdescribed.

In view of the above, it will be seen that the several advantages of thedisclosure are achieved and other advantageous results attained. Asvarious changes could be made in the above processes and compositeswithout departing from the scope of the disclosure, it is intended thatall matter contained in the above description and shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. An alkaline electrochemical cell comprising: acathode; a gelled anode mixture, the mixture comprising an anode activematerial, a gelling agent, and an alkaline electrolyte, wherein theanode active material has an apparent density of from about 2.50 g/cc toabout 3.00 g/cc and wherein the anode active material comprisesparticles having an aspect ratio of from about 10.0 to about 50.0; and,a separator between the cathode and the anode.
 2. The cell of claim 1,wherein the anode active material has an apparent density of from about2.65 g/cc to about 2.85 g/cc.
 3. The cell of claim 1, wherein from about5% to about 35%, by weight, of the total anode active material presentin the gelled anode mixture has a particle size of less than about 75microns.
 4. The cell of claim 1, wherein the anode active materialcomprises a zinc alloy.
 5. The cell of claim 4, wherein the zinc alloycomprises indium and bismuth.
 6. The cell of claim 5, wherein the zincalloy comprises from about 80 ppm to about 250 ppm of bismuth and fromabout 80 ppm to about 250 ppm of indium.
 7. The cell of claim 1, whereinthe gelled anode mixture further comprises a gassing inhibitor.
 8. Thecell of claim 7, wherein the gassing inhibitor is present in the gelledanode mixture in an amount of from about 10 ppm to about 150 ppm.
 9. Thecell of claim 7, wherein the gassing inhibitor is a phosphate ester. 10.The cell of claim 1, wherein the electrolyte has a hydroxideconcentration of about 30% or less.
 11. A gelled anode mixture, themixture comprising an anode active material, a gelling agent, and analkaline electrolyte, wherein the anode active material has an apparentdensity of from about 2.50 g/cc to about 3.00 g/cc and wherein the anodeactive material comprises particles having an aspect ratio of from about10.0 to about 50.0.
 12. The gelled anode mixture of claim 11, whereinthe anode active material has an apparent density of from about 2.65g/cc to about 2.85 g/cc.
 13. The gelled anode mixture of claim 11,wherein from about 5% to about 35%, by weight, of the total anode activematerial present in the gelled anode mixture has a particle size of lessthan about 75 microns.
 14. The gelled anode mixture of claim 11, whereinthe anode active material comprises a zinc alloy.
 15. The gelled anodemixture of claim 14, wherein the zinc alloy comprises indium andbismuth.
 16. The gelled anode mixture of claim 15, wherein the zincalloy comprises from about 80 ppm to about 250 ppm of bismuth and fromabout 80 ppm to about 250 ppm of indium.
 17. The gelled anode mixture ofclaim 11, wherein the gelled anode mixture further comprises a gassinginhibitor.
 18. The gelled anode mixture of claim 17, wherein the gassinginhibitor is present in the gelled anode mixture in an amount of fromabout 10 ppm to about 150 ppm.
 19. The gelled anode mixture of claim 17,wherein the gassing inhibitor is a phosphate ester.
 20. The gelled anodemixture of claim 11, wherein the electrolyte has a hydroxideconcentration of about 30% or less.